This invention relates generally to liquid crystal display (LCD) systems and particularly to a display system of the type described wherein ambient light is channeled for illuminating the LCD. That is to say, ambient light in the forward field of an observer is channeled to the rear of the LCD to provide an image contrast ratio independent of the brightness of the ambient light whereby the display is enhanced.
Liquid crystal display systems are used, for example, for displaying navigational or strategic flight information in the field of vision of the pilot of an aircraft. In military applications the LCD system is mounted on the aircraft pilot's helmet.
LCD systems particularly for the purposes indicated use backlighting to provide illumination for the LCD under conditions of low to very high ambient light brightness. The backlighting approach works well until ambient light brightness levels in the 2,000 to 10,000 foot lambert range are encountered. Under these conditions the backlighting brightness levels required are difficult to maintain and require high power levels. The present invention overcomes this difficulty by utilizing ambient light. The ambient light is channeled to the rear of the LCD to provide a defined contrast light ratio. Under required conditions a supplementary illuminator is used in conjunction with the channeled ambient light.